Users of data communications continue to demand ever faster service. Acoustical modems are typically able to deliver a maximum of fifty six thousand bits per second (kbps). Higher speed broadband connections have encouraged content providers to provide services that are not practical at lesser speeds, typically requiring a minimum of 150 kbps. Digital Subscriber Lines (“DSL”) offer speeds up to several megabits per second (Mbps), depending upon distance from the telephone service provider's Central Office (“CO”) to the Customer Premises Equipment (“CPE”) and the user's willingness to pay a premium. At certain distances high speed DSL is not available at any reasonable price simply because the technology is not able to do so. Typically consumer speed DSL is not offered by the telecommunications companies at greater than about 2.5 miles from the CO. Thus the service area of providers is limited by the number of COs and their proximity to each other. This limit is the result of DSL vendors' utilization of the existing unshielded twisted pair (“UTP”) copper wire network that has been the mainstay of the telephone infrastructure from the inception of commercial telephony. An advantage of UTP is that it is into virtually every home and business by virtue of its use for carrying ordinary telephone connections. A disadvantage of UTP is that it is not well suited for high frequency signals in that the high frequencies necessary for the data rates desired are strongly attenuated by the wire media itself. This is the result of the build up of impedance with wire length.
A competing broadband service is offered by television cable companies, wherein optical fiber service is installed into a neighborhood. A limited number of subscribers may then share the total bandwidth available up to approximately 1.25 miles from the termination end of the fiber connection via coaxial wire. Cable broadband speeds are often over 1 Mbps. To compete with the cable providers for broadband coverage as well as speed, the DSL providers are forced to also install more fiber connections, farther away from the CO, from which the DSL UTP lines may spawn. The installation of fiber is very costly in terms of labor, materials, and in some cases access rights. Though in the United States broadband cable currently has more market share than DSL, total market penetration of broadband service is very small. Thus the competition for share is very open.
There would be economic and time to market advantage to the DSL providers if they could economically extend their market coverage with the existing UTP infrastructure and do so at a data rate that is competitive with broadband cable. The prior art has been largely based upon repeaters which receive the DSL signal, decode it using the pertinent protocol for error detection and correction, then reformulate the data and retransmit it with a rejuvenated signal. Such approaches are very costly. Other products of the relevant art utilize the UTP infrastructure but require the telecommunications companies to install different equipment at the CO and CPE, which is expensive.
The present invention provides for the extension of the DSL service range via existing UTP lines with no change of equipment or software at the CO or at the CPE, often with a higher data rate than currently available. It is an objective of the present invention to enable DSL service providers to economically extend their market coverage, compete with broadband cable providers in terms of speed, and to enable them to roll out coverage and service improvements more rapidly than broadband cable suppliers due to lower capital needs for infrastructure extension.
DSL technology is based upon a bidirectional connection between a Digital Subscriber Line Access Multiplexer (“DSLAM”) board at the CO and a DSL modem at the customer's premises. There is a one for one relationship. That is, a single, dedicated set of twisted pair wires extends from a single port on the DSLAM to the customer's DSL modem. No other subscriber is served by that same set of wires. A splitter at or near the premises entry point divides the frequency spectrum assigned to the analog voice signal (if present) from the spectrum dedicated to DSL use. The lower 30 khz is reserved for the voice signals. The DSL signals are assigned one or more separate, non-overlapping frequency bands for the “uplink” (towards the CO) direction and one or more non-overlapping frequency bands for the “downlink” (towards the CPE) direction. The data flowing in these two directions are independent of each other and flowing simultaneously, just in different directions through the same media at the same time, separated by frequency, not by time. Thus any device that is inserted between the premises splitter and the CO DSLAM must accommodate signals ranging from near dc to 1100 khz or more, without regard to direction, where “direction” distinguishes at which end of the connection is the transmitter (at the CPE for the uplink, at the CO for the downlink) and at which end is the receiver (at the CPE for the downlink, at the CO for the uplink).
The Asymmetrical DSL (“ADSL”, ADSL meaning the downlink data rate is not the same as the uplink data rate) and Symmetrical DSL (“SDSL”) standards for transmission are for the voice, uplink, and downlink signals to be present on the UTP simultaneously. This is in contrast to High Bit Rate DSL (“HDSL”) wherein the downlink data is applied to one UTP set, the uplink to another UTP set, and the voice data is not carried at all by the system. The industry standard (described in ANSI T1.417 and others) segregates various categories of data by frequency range.
In the 1100 khz bandwidth of the G.992.1 (ADSL) standard there are two hundred and fifty six 4.3125 khz “buckets”. The signal present on an ADSL physical wire line is called a Digital Multi-Tone (DMT) because it is comprised of the energy of different frequency tones. The higher frequency buckets of the DMT signal suffer greater attenuation as UTP wire line length increases. Consequently, the higher frequency buckets are hampered in their ability to effectively carry data relative to those buckets of lower frequency.
For ADSL, the portion of the bandwidth from approximately 0 Hz (bucket 0) to 30 khz (bucket 7) is reserved for the voice channel and other signaling. The portion of the bandwidth from approximately 34 khz (bucket 8) to 125 khz (bucket 29) is assigned to the ADSL upstream channel, thus comprising the next 22 buckets. As UTP wire line increases in length, fewer upstream buckets are able to carry data, resulting in a reduction in upstream data rate.
The portion of the bandwidth from approximately 164 khz (bucket 38) to 1100 khz (bucket 255) is assigned to the downstream channel, thus comprising the upper 218 buckets. As UTP wire line increases in length, fewer downstream buckets are able to carry data, resulting in a reduction in downstream data rate. The data rate is negotiated between the CO and the CPE.
Beyond approximately 18,000 feet of commonly used UTP phone wire, most of the corresponding bandwidth is so attenuated, with most downstream buckets rendered useless, that communication per the ADSL standard ceases altogether.
In the general case, any number of non-overlapping frequency bands may be assigned for uplink and downlink data, presumably the two being interleaved. For example, FIG. 1 illustrates a generalized assignment scheme for interleaved DSL. FIG. 2 illustrates the frequency band assignment standard for ADSL, wherein only one band (34 khz to 125 khz) is assign to uplink data and only one band (164 khz to 1100 khz) is assigned to downlink data. The spectrum above 1100 khz is not utilized. Other standards are evolving that may assign somewhat different frequency blocks and/or utilize a higher maximum frequency. One skilled in the art will understand that the present invention is applicable to such different frequency assignments by selecting different component values for the various circuit blocks described herein such that they are tuned to filter out or pass or amplify in the appropriate frequency ranges.
The present invention operates on ISO OSI model Layer 1. That is, it is a purely analog device with no software or comprehension of protocols or frames. It takes a weak, noisy signal, cleans it up and amplifies it. Thus it is useful regardless of what protocol the signals may represent. Those skilled in the pertinent art will understand its applicability in improving signal quality within any UTP transmission system.